In the medical treatment of various diseases, e.g. in the cardiovascular, gastrointestinal and chemotherapeutic field, it is an advantage to have a constant concentration of the administered drug in the blood. Thus a controlled release of the drug from the pharmaceutical preparation is wanted.
It is important that the controlled release preparation delivers the amount of drug needed to maintain an adequate and even effect during the entire therapeutic dosage interval. This usually means that the drug should be delivered at a constant rate to give an even concentration of the administered drug in the blood which is of specific importance for drugs having a small therapeutic index, i.e. a small difference between effective and toxic concentration. A delayed and constant release of the drug will also be of importance for locally irritating drugs having a potential risk of causing gastrointestinal disturbances when present in large local concentrations or for drugs having a short elimination half-life. In the latter case less frequent administration and thus better patient compliance (cf. Hayes R. B. et al. Clin. Pharm. Therap. (1977), 22, pp. 125-130) may be obtained with controlled release preparations compared with conventional dosage forms.
A drug can be delivered in a controlled way via any route of administration but the preparations should preferably have some features in common, e.g. give a controlled and reproducible release of drug and contribute to a reproducible absorption, have no toxic or irritating constituents and be suitable also for high dosage drugs.
Examples of drug delivery systems for oral use with a controlled release of the drug are e.g. sustained release tablets of the insoluble matrix type, such as Durules.RTM., and the osmotically active tablet, OROS.RTM.. The OROS.RTM. system is described in U.S. Pat. No. 4,036,227 and in a supplement to British Journal of Clinical Pharmacology (1985), 19, 695-765 by Theeuwes F. et al. It consists of a tablet core of the drug substance as the major constituent which is surrounded with a semipermeable polymeric membrane through which a small opening is drilled. DE-A-2030501 describes a preparation of the matrix type which contains amorphous silicon dioxide. The active compound is released by diffusion through the matrix. The examples above are single-unit systems with all drug substance concentrated in one unit while the present invention is of the multiple-unit principle.
From GB-A-1542414 a composition is known containing an organic support material to which an active compound is physically or chemically bound and a glass material in contact with said support material. The glass contains soluble metal ions. The release of drug is governed by the dissolution of metal ions from the glass material due to an ion exchange process. Obviously, the glass is not an insoluble inert compound of the composition.
Several advantages with depot preparations comprising a large number of small units have been described in the literature. It is, for example, possible to obtain a reproducible emptying of the units from the stomach into the small intestine when the particles are less than 1-2 mm (cf. Bogentoft C. et al: Influence of food on the absorption of acetylsalicylic acid from enteric coated dosage forms. Europ. J. Clin. Pharmacol. (1978), 14, 351-355). Dispersion over a large area in the gastrointestinal canal can give a more reproducible total time for the passage, which is of advantage for the absorption process (cf. Edgar B. et al: Comparison of two enteric-coated acetylsalicylic acid preparations by monotoring steady-state levels of salicylic acid and its metabolites in plasma and urine. Biopharmaceutics & Drug Disposition, (1984), 5, 251-260). In addition a multiple unit preparation is preferable to one single drug unit as the dose is spread out in the intestine. The risk of local irritation and accumulation of several doses due to constriction in the alimentary canal are also considered to be lower, (cf. McMahan F. G. et al: Upper gastrointestinal lesions after potassium chloride supplements: A controlled clinical trial The Lancet, Nov. 13, 1059-1061).
A further advantage with a multiple unit preparation is that it may be divided into smaller portions all having the same absorption properties. This makes it possible to obtain a greater flexibility in selecting the size of the dose.